1. Field of the Invention
The present invention relates to a magneto-resistance effect element and a thin-film magnetic head which are suitably used for a hard-disk drive, and to a method for manufacturing the magneto-resistance effect element.
2. Description of the Related Art
A hard-disk drive uses a thin-film magnetic head having a magneto-resistance effect element (MR element) to read out a magnetic signal. In recent years, the trend is for hard-disk drives to have higher recording densities. Correspondingly, the magneto-resistance effect element in a thin-film magnetic head is required to have, in particular, higher sensitivity and higher output.
A CIP-GMR (Current in Plane-Giant Magneto-resistance) element which is a giant magneto-resistance effect element having a nonmagnetic layer between ferromagnetic layers and passing a sensing current in parallel to a layer surface, has been conventionally developed as a reproducing element in a thin-film magnetic head. On the other hand, a magnetic head that uses a TMR (Tunnel Magneto-resistance) element which has an insulation layer instead of the nonmagnetic layer as an intermediate layer and which passes a sensing current perpendicular to a layer surface, has also been developed in order to achieve higher densification. Furthermore, a magnetic head that uses a CPP (Current Perpendicular to Plane)-GMR element which is a GMR element having a nonmagnetic layer as the intermediate layer and passing a sensing current perpendicular to the layer surface similar to the TMR element, has also been developed. CPP-GMR element has an advantage of having low resistance in comparison with the TMR element and higher output in a narrower track width than the CIP-GMR element.
FIG. 1 shows a structure of the conventional CPP-GMR element. CPP-GMR element 104 is interposed between lower shield layer 113 and upper shield layer 115, each of which serves as an electrode film as well, and is also referred to as a spin valve film (SV film). CPP-GMR element 104 has a pillar shape having a desired size, and has a structure in which nonmagnetic spacer layer 144 is interposed between pinned layer 143 that is a ferromagnetic layer in which the magnetization direction is fixed and free layer 145 that is a ferromagnetic layer in which the magnetization direction varies according to an external magnetic field. The magnetization direction in the pinned layer 143 is fixed because pinned layer 143 is arranged on antiferromagnetic layer 142 arranged thereon. Recently, pinned layer 143 can be not only made into a single-layered structure of a ferromagnetic material but can also be made into a three-layer structure (synthetic pinned layer) formed of a ferromagnetic layer that is inner layer 143c, a nonmagnetic metal layer that is nonmagnetic intermediate layer 143b, and a ferromagnetic layer that is outer layer 143a. Thus configured, CPP-GMR element 104 provides a strong exchange coupling between two ferromagnetic layers 143a and 143c, and thus effectively increases the power of exchange coupling with antiferromagnetic layer 142. Hard magnetic film (hard bias film) 148 made from CoPt or CoCrPt is arranged around CPP-GMR element 104 through insulation film 147 such as Al.sub.2O.sub.3. Hard bias film 148 is a film for controlling the magnetic domain of free layer 145, and is located on the side of CPP-GMR element 104 in the track width direction. Cap layer 146 and buffer layer 141 are respectively arranged on the top end and the bottom end of CPP-GMR element 104. Cap layer 146, CPP-GMR element 104, and buffer layer 141 are interposed between upper shield layer 115 and lower shield layer 113.
Feature of low resistance of a CPP-GMR element is very advantageous for frequency characteristics, but causes a defect that resistance change is low. This is because when the absolute value of resistance is small, the amount of resistance change is generally small as well. The magneto-resistance effect element having a small amount of the resistance change shows low sensitivity when used as a reproducing element in a thin-film magnetic head.
For this reason, a known CPP-GMR element uses the technology of CCP (Confined Current Path) to increase the resistance value by restricting electric current.
Japanese Patent Application Laid-Open No. 2002-208744 describes a configuration in which a resistance adjustment layer is arranged on at least one of a pinned layer, a spacer layer, and a free layer. For instance, the resistance adjustment layer which is made from a metalloid or a zero-gap semiconductor and which has a pinhole therein, is inserted into each of the layers. In the configuration, an electric current that flows in a direction perpendicular to a layer surface is interrupted by the resistance adjustment layer, and only flows through the pinhole in the resistance adjustment layer. Japanese Patent Application Laid-Open No. 2003-204094 proposes a configuration in which a magnetic metal and an insulative material are distributed on a boundary surface of the spacer layer. The magnetic metal and the insulative material interrupt the electric current flowing in a direction perpendicular to the layer surface. Accordingly, the electric current only passes through gaps which lack magnetic metal and insulative material. As thus described above, in the configurations of Japanese Patent Application Laid-Open No. 2002-208744 and Japanese Patent Application Laid-Open No. 2003-204094, electric current flowing in the direction perpendicular to the layer surface only passes through specific parts (that are pinholes or gaps) inside the spacer layer. In other words, the spacer layer has a function of restricting electric current by confining the path for the electric current to pass, and consequently increases the resistance value.
In addition, Japanese Patent Application Laid-Open No. 2005-136309 proposes a configuration in which a spacer layer is partially irradiated with an Ar ion beam and then the spacer layer is oxidized. As a result, a region which has been previously irradiated with the Ar ion beam, becomes a current control region for passing an electric current in a direction perpendicular to a layer surface. The region which has not been previously irradiated with the Ar ion beam becomes an insulator region for interrupting the electric current in the direction perpendicular to the layer surface. In the configuration described in Japanese Patent Application Laid-Open No. 2002-176211, a stacked body of a pinned layer, a spacer layer, and a free layer are partially oxidized from the side of the stacked body. As a result, there exists an oxidized region for interrupting the electric current in the direction perpendicular to a layer surface, in both sides of each layer; and there remains a non-oxidized region for passing the electric current in the direction perpendicular to the layer surface, in the central part of each layer. Thus, in the configurations of Japanese Patent Application Laid-Open No. 2005-136309 and Japanese Patent Application Laid-Open No. 2002-176211 as well, the electric current in the direction perpendicular to the layer surface only passes through a specific part (that is current control region or non-oxidized region) inside the spacer layer. In other words, the spacer layer has a function of restricting the electric current by confining the path for the electric current to pass, and consequently increases a resistance value.
As described above, in configurations according to the above described four patent documents, a spacer layer increases a resistance value by the function of confining electric current, and thereby increases the amount of resistance change.
In a CCP-CPP-GMR element, an electric current value in a direction perpendicular to a layer surface varies, in other words, a resistance value varies according to the size of a current confining part. The amount of resistance change is dependent on the change of the electric current, and furthermore, the sensitivity of the magneto-resistance effect element is also dependent on the change of the electric current. Accordingly, in order to obtain a magneto-resistance effect element having the desired sensitivity, the current confining part needs to be formed with high accuracy.
In a configuration described in Japanese Application Patent Laid-Open No. 2002-208744 among the above described conventional CCP-CPP-GMR elements, a resistance adjustment layer of an aluminum oxide layer having pinholes is formed, for example, by the steps of forming an aluminum layer and exposing the aluminum layer to an oxygen atmosphere to make self oxidation. The resistance adjustment layer can also be formed by another method comprising the steps of forming one or more copper pillars on a copper layer that makes up the spacer layer; and filling a perimeter of the pillar with an insulation material (oxide, for instance). The resistance adjustment layer can also be formed by still another method comprising the steps of forming an insulative layer that has previously opened pinholes on the copper layer that makes up the spacer layer. However, it is very difficult to form a resistance adjustment layer having pinholes with the appropriate number and size uniformly distributed therein by these methods.
In addition, in Japanese Patent Application Laid-Open No. 2003-204094, the configuration is formed, for instance, by the steps of preparing a copper layer as a spacer layer, forming a magnetic metal film by sputtering, and introducing oxygen gas, so that an insulative material which makes up oxidized parts and a magnetic metal which makes up unoxidized parts are distributed in a mixed state. In this method, it is difficult to precisely and uniformly distribute the oxidized parts of the insulative material, and to precisely and uniformly distribute the unoxidized parts of magnetic metal without being oxidized, in the magnetic metal film at an appropriate ratio.
In a configuration described in Japanese Patent Application Laid-Open No. 2005-136309, it is necessary to irradiate Ar ion beam with high accuracy, and to completely oxidize a part which has not been irradiated with the Ar ion beam. When the Ar ion beam has been irradiated with low accuracy, or when the part which has not been irradiated with the Ar ion beam remains insufficiently oxidized, a current confining part can not be formed with high accuracy, and the obtained magneto-resistance effect element does not show the desired sensitivity.
In the configuration described in Japanese Patent Application Laid-Open No. 2002-176211, when a SV film is oxidized (or nitrided or oxynitrided) up to an inaccurate depth from the side of the SV film, a current confining part can not be formed with high accuracy, and the resulting magneto-resistance effect element does not show the desired sensitivity.
A recent magneto-resistance effect element is so small that the length of one side is about several tens of nanometers. Accordingly, it is difficult to form a highly precise current confining part inside a spacer layer of the magneto-resistance effect element by the methods described in the above four patent documents. In other words, it is very difficult to form extremely fine pinholes with high accuracy based on the method of Japanese Patent Application Laid-Open No. 2002-208744, to oxidize a magnetic metal film at an appropriate ratio based on the method of Japanese Patent Application Laid-Open No. 2003-204094, to precisely irradiate an ion beam and completely oxidize an unirradiated part based on the method of Japanese Patent Application Laid-Open No. 2005-136309, and to precisely oxidize (or nitride or oxynitride) an SV film from the side of the SV film by the desired depth based on the method of Japanese Patent Application Laid-Open No. 2002-176211. Accordingly, it is actually difficult to obtain the desired current confining effect and the desired sensitivity in an extremely fine magneto-resistance effect element by the four methods. Besides, in the configurations described in those patent documents, an unprecedented, special, and complicated step must be done for the purpose of forming the current confining part. As a result, the manufacturing cost increase.